Nondestructive ultrasonic testing of the material health of composite materials is known from the prior art. Such methods are advantageously implemented by ultrasound generated by a thermoelastic excitation of the surface of the parts made from these materials, created by localized and rapid heating of the surface with a laser beam, an energy comprised between 1 and 5 joules·cm−2 being deposited on the surface. The composite materials of concern by the method of the disclosure are made up of reinforcing fibers in a thermoplastic or thermosetting organic matrix such as an epoxy resin. It is this resin that absorbs the laser radiation and the response of which to this excitation produces thermoelastic effect that gives rise to the ultrasonic mechanical wave, the analysis of the propagation of this wave in the material allowing the nondestructive test to be carried out. In order for this effect to be possible, the light energy deposited on the surface must be absorbed by a sufficient volume of resin in order for the light energy to be converted into mechanical energy before the laser beam reaches the reinforcements. Specifically, if the reinforcements are touched by the light wave, they produce flashes, thereby degrading the reinforcement and possibly even vaporizing the surrounding resin.
Thus, the amount of energy deposited on the surface of the part by each shot must be adjusted depending on the thickness of resin separating the first reinforcements from the surface of the part.
In the prior art, the excitation power of the laser generating the ultrasonic wave is adjusted on a control sample of the material making up the part to be tested or on a representative zone of the part. The parameters of the laser shots are then adjusted by visual inspection and based on the experience of the operator, and are kept constant for the inspection of the entire part. Nevertheless, more particularly for large parts, the external resin layer of the latter may contain thickness variations or may even be missing in places. Under these conditions, flashes of light are liable to be generated during the testing of the part even though the parameters of this test were adjusted beforehand on a sample.